[Argonavis (William)]

Originally Posted by Don Pensack

My 5 and 7mm Naglers display coma in their outer fields, so I use a Paracorr for every eyepiece. But they exhibited only annoying, and somewhat minor comatic images at the edge.
My 35 Panoptic, on the other hand, exhibited a starfield that looked like I was standing on the deck of the Millenium Falcon going to lightspeed. The star images looked like radial streaks.

The Nagler are designed to handle the fast light cone from an f4 or f5 scope - so of course they will display less coma. That's why you pay so much money for them.

So I am not sure your comparison is valid. I believe you would need to compare different magnifications of the same ocular design to test whether coma is a function of magnification.

Originally Posted by Don Pensack

Here's what I think: Star images are not magnified. They appear the same size in all eyepieces until the Airy Disc is visible, and then start appearing larger. The 5mm eyepiece is a 1mm exit pupil in my scope, yet represents my highest magnification (I'm not a planets or double stars observer, so powers above 400X aren't too useful to me, on an undriven scope), but that magnification *just* makes the Airy disc visible.

I remember one night using x600 on an undriven 20inch f5. The seeing was exceptional and supported this magnification. It is worth keeping a shortish focal length ocular in your kit for such nights.

and it doesn't seem to make a lot of sense that star images are not magnified, then suddenly they are once the Airy disk becomes visible.

Originally Posted by Don Pensack

Accordingly, the only factor having an influence on what coma I see is field stop size in millimeters--a wider field stop will display more coma and magnification has nothing to do with it.

I suspect both have an effect, along with f ratio and eyepiece design. The combined effect, together with the observers individual variation in visual perception and experience, would be difficult to model. Which is why we have this discussion with Bratislav leaving.

I am sure "Optics 101" says one thing, and the observers eye adds another layer of complexity. We all seem to perceive or react differently to the image presented to us through an ocular. My view is that there is a layer of emotional perception that everyone applies to what they see visually.

That what I think.